2030981 - Use DOM-accessible data storage for maplike/setlike

Status: NEW

(Core :: DOM: Bindings (WebIDL), task)

Description

[Jan Jaeschke [:jjaschke]]

Currently, our implementation for the maplike/setlike webidl concepts use Spidermonkey datastructures to store the data. This makes it inaccessible from DOM code, leading to parallel data structures, which is both inefficient and error prone.

Comment 1

[Jan Jaeschke [:jjaschke]]

Attachment: Bug 2030981, part 1 - Implement ECMA{Set|Map} in Gecko. r=edgar!

Comment 2

[Jan Jaeschke [:jjaschke]]

Attachment: Bug 2030981, part 2 - Introduce [DOMBackedStorage] for WebIDL setlike/maplike, provide SetlikeMixin/MaplikeMixin. r=edgar!

Previously, WebIDL setlike/maplike interfaces were backed by a JS Set/Map
stored in a reserved slot, making their data inaccessible from C++. Every
interface had to maintain a parallel C++ mirror and manually keep it in sync.

This patch introduces the [DOMBackedStorage] WebIDL extended attribute as an
explicit opt-in that switches a setlike/maplike declaration to use a C++-owned
ECMASet/ECMAMap as the backing store. Interfaces that opt in must inherit
SetlikeMixin<T> or MaplikeMixin<K, V> directly to expose SetData()/MapData().

• CGECMACollectionMethodGenerator generates method bodies that call directly
  into the C++ data structure for [DOMBackedStorage] interfaces
• Physical-index iterators (ECMACollectionIterator.h) provide ES-compatible
  mutation-during-iteration semantics
• Interfaces without [DOMBackedStorage] continue to use the JS-backed path